To illustrate the performance characteristics, Seymour and Isaacs (1974) 

 generalized the described process by specifying an arbitrary spectrum, the 

 Pierson-Moskowitz model (Pierson and Moskowitz, 1963). The equations govern- 

 ing this spectrum are such that the spectrum can be uniquely specified by the 

 frequency at which the peak energy, f , is found. From this, the deepwater 



wavelength, L , is calculated as 



P' 



L P 2TT(f ) 2 



(69) 



The wavelength at which the peak energy is found can be used to develop two 

 dimensionless ratios which define the breakwater: df/L , the ratio of float 

 diameter-to-peak wavelength and d/L , the ratio of water depth-to-peak wave- 

 length. A digital computer search of df/L and d/L space will determine 

 the required number of rows of floats to achieve a desired level of wave 

 height reduction. For an assumed float density of 4 percent, with the anchor 

 assumed to be on the bottom, and for a float just below the surface, Seymour 

 and Isaacs (1974) present example performance estimations which determine the 

 number of rows of floats to provide 75-, 50-, and 25-percent wave height 

 reduction (Figs. 115, 116, and 117, respectively). 



80 r 



60 



40- 



m 20- 



Curve 

 I 



2 

 3 

 4 

 5 

 6 



Diameter to 

 wavelength 

 ratio, d^/L 

 0.035 P 



FLOAT DENSITY 

 WATER DENSITY 



- = 0.04 



0.2 04 0.6 08 1.0 1.2 1.4 

 RATIO OF DEPTH -TO-DEEPWATER WAVELENGTH AT PEAK ENERGY, d/L 



Figure 115. Performance estimation of tethered-f loat breakwater at 

 a theoretical 75-percent wave height reduction (after 

 Seymour and Isaacs, 1974). 



170 



